fixed a bug where -0.5 / -epsilon triggers UB

MichaelSuen-thePointer · May 10, 2024 · 5f57cf4 · 5f57cf4
1 parent 9810a17
commit 5f57cf4
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Showing 2 changed files with 5 additions and 2 deletions.
diff --git a/include/fixmath/fixed_impl.inl b/include/fixmath/fixed_impl.inl
@@ -294,8 +294,10 @@ constexpr fixed<policy> operator/(fixed<policy> a, fixed<policy> b) {
 	int64_t rem = 0;
 	if constexpr (sizeof(raw_t) == 8) {
 		// use extended int128 division
-		raw_t _check_bits = a.raw() >> (fixed::ALL_BITS - fixed::FRACTION_BITS - 1); // check for simple division
-		if (FIXMATH_LIKELY(_check_bits == 0 || _check_bits == -1)) {
+		raw_t _check_bits = a.raw() >> (fixed::ALL_BITS - fixed::FRACTION_BITS - 1);
+		raw_t _remain_bits = a.raw() & (fixed::FRACTION_MASK >> 1);
+		if (FIXMATH_LIKELY(_check_bits == 0 || (_check_bits == -1 && _remain_bits))) {
+			// check for simplified division
 			qlo = a.raw() * fixed::RATIO;
 			if constexpr (policy::rounding) {
 				rem = qlo % b.raw();

diff --git a/tests/unit_tests.cpp b/tests/unit_tests.cpp
@@ -267,6 +267,7 @@ TEST(FIXMATH, DIV) {
 	CHECK_FIX_DIV(ABSERROR, -ABSERROR);
 	CHECK_FIX_DIV(-1.234, -4.321);
 	CHECK_FIX_DIV(-1.234, 4.321);
+	EXPECT_EQ(-Fix32(0.5) / -Fix32::epsilon(), Fix32::max_sat());
 	EXPECT_EQ(1 / Fix32::epsilon(), Fix32::max_sat());
 	EXPECT_EQ(1 / -Fix32::epsilon(), Fix32::min_sat());
 	EXPECT_EQ(Fix32::max_fix() / Fix32(0.5), Fix32::max_sat());